Safety weight control and compensating apparatus for subsurface well bore devices



Nov. 24, 1964 A. w. KAMMERER 3,158,208

SAFETY WEIGHT CONTROL AND COMPENSATING APPARATUS FOR SUBSURFACE WELL BORE DEVICES Filed April 6, 1962 3 Sheets-Sheet 1 E RIG. 2,

Reservoir INVENTOR.

flea/E2 W Ida/144452519 firroewsy.

Nov. 24, 1964 A. w. KAMMERER 3, 5

SAFETY WEIGHT CONTROL AND COMPENSATING APPARATUS FOR SUBSURFACE WELL BORE DEVICES Filed April 6, 1962 3 Sheets-Sheet 2 Page! v01 INVENTOR.

fllecwse PK KHMMEEER flrroelve Y- 1964 A. w. KAMMERER 3,

SAFETY WEIGHT CONTROL AND COMPENSATING APPARATUS FOR SUBSURF'ACE WELL BORE DEVICES Filed April 6, 1962 7 3 Sheets-Sheet 3 i l3 .INVENTOR.

5 flea/E2 W KAMMEEEE 14 TroRA/EY- United States Patent SAFETY WEEGHT CGNTROL AND C@MPENAT- ENG APPARATUS FOR SUBSUEL ACE WELL BGRE DEVHCES Archer W. Kammerer, 869 N. Raymond Ave, Fullerton,

Qaiii, assignor of one-fifth to Jean K. Lamphere, Fullerton, Caliitl, and one-fifth to Archer W. Kamrnerer, in, Houston, Tex.

Filed Apr. 6, 1962, Ser. No. 185,554 19 Claims. (Cl. 175-27) The present invention relates to apparatus for controllably supporting a running-in string in a well bore, such as a tubular string of drill pipe, tubing or casing.

In United States Patent No. 2,945,676, an apparatus is disclosed that automatically and hydraulically maintains a substantially constant tension in a running-in string disposed in a well bore. In the event of sudden loss of hydraulic pressure in its system, such as caused by breaking of a hydraulic line, control of the running-in string would be lost, with potential resulting damage to the equipment.

Accordingly, it is an object of the present invention to provide a hydraulic apparatus for maintaining a substantially constant tension in a running-in string, in which loss of hydraulic pressure cannot result in damage to the equipment.

Another objector" the invention is to provide a hy draulic compensating apparatus for maintaining a substantially constant tension in a running-in string disposed in a well bore, in which the apparatus prevents a sudden drop of the running-in string in the well bore in the event of excessive loss of fluid pressure in the hydraulic system.

A further object of the invention is to provide a hydraulic compensating apparatus for maintaining a substantially constant tension in a running-in string disposed in a well bore, in which the apparatus prevents any substantial lowering or dropping of the running-in string in the well bore in the event of damage to the hydraulic system of the apparatus.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of several forms in which it may be embodied. Such forms are shown in the drawings accompanying and forming part of the present specification. These forms will now be described in detail for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

FIGURE 1 is a diagrammatic view of one application of the invention;

FIG. 2 is a diagrammatic view of a safety weight control and compensating apparatus forming part of the equipment disclosed in FIG. 1;

FIG. 3 is a view similar to FIG. 2 of another embodiment of the invention;

FIG. 4 is a longitudinal section through a pressure volume check valve incorporated in the apparatus disclosed in FIG. 3;

1G. 5 is a longitudinal section through another em bodiment of weight control and compensating apparatus;

FIG. 6 is an enlarged cross-section taken'along the line 6-6 on FIG. 5;

FIG. 7 is an enlarged cross-section taken along the line 7 77 on FIG. 5;

FIG. 8 is a longitudinal section through a pressure volume check valve incorporated in the apparatus dsclosed in FIG.5 V

In the dihwingg several specific forms of weight control and compensating apparatus A are illustrated as being applied to the drilling of a well bore B. The appa ratus is disposed above ground, or above the surface of the water, as illustrated in FIG. 1, and in a convenient position within a drilling rig, as,.for example, between the traveling block T and an adjacent lower swivel S. The drilling rig may be mounted on land, or on a floating drilling barge C, appropriately anchored in place and floating in a body of water W, such as ocean water,

through which the well bore is to be drilled commencing at the fioo r'F of the ocean. The traveling block T has the usual lines L passing therethrough, which also pass over a crown block E at the upper end of the derrick D, suitably secured in place on the floating barge. The swivel S, which may be of any desired type, is connected to a running-in string, such as a string of drill pipe P, the upper portion of which is constituted as a kelly or grief stem K slidably splined to the rotary table R of the apparatus for the purpose of rotating the drill stem P and a drill bit H connected to its lower end. As is usual in the rotary drilling of well bores, suitable drilling fluid is pumped down the string of drill pipe P, discharging from the drill bit H and carrying the cuttings upwardly out of the hole B.

The weight control and compensating apparatus A illustrated in FIG. 2 includes a cylinder 10 of the required length and cross-sectional area, having an upper cylinder head 11 and a lower cylinder head 12., the lower head being provided with a suitable connection 13, such as an eye, by means of which it is attached to the upper portion of the rotary swivel S. A piston 14 is reciprocably mounted in the cylinder 16 the piston being secured to a piston rod 15 extending upwardly through the upper cylinder head 11 and having a suitable eye or bail 16 at its upper end to receive the hook I of the traveling block T. To prevent leakage from the cylinder, a rod packing 17 is provided in the upper cylinder head 11, which slidably and sealingly engages the piston rod 15; whereas, a suitable packing or seal ring 18 is mounted on the piston 14 to prevent leakage therearound, the seal ring sealingly engaging the wall of the cylinder.

The cylinder 10 is filled with a suitable liquid, such as oil, completely between the piston 14 and the upper cylinder head 11. The liquid is derived from a suitable reservoir 19 connected to a motor driven pump 20, preferably of a high pressure centrifugal type, the liquid discharging from the pump through an inlet line 21 opening into the upper portion of the cylinder 10. An outlet line 22 is also connected to the upper portion of the cylinder It), for the purpose of returning the liquid to the reservoir. The outlet line includes a choke orifice 23 to enable back pressure to be built up in the inlet line 21 and cylinder 10 above the piston 14, so that liquid under a desired pressure is maintained in the cylinder space 24 above the piston to enable the cylinder it) to be supported by the piston through the liquid medium.

The apparatus A constitutes a telescopic joint for supporting a portion or all of the weight of the running-in string or drill string P. The drill string is suspended from the swivel S, which is carried by the cylinder lltl, the load being transferred from the upper cylinder head 11 through the liquid medium in the upper cylinder space 24 to the piston 14 and piston rod 15, and from the latter to the traveling block T and the usual lines L connected in a known manner to the draw works (not shown) and passing over the crown block E.

The pressure of the liquid in the cylinder space 24- determines the lifting force on its cylinder head 11 and on the drill string P that extends downwardly from and is connected through the swivel S to th ylinder 10. The greater the pressure, the greater is the lifting force; whereas, the lesser the pressure, the less will be the lifting force. Accordingly, by controlling the liquid pressure in the cylinder space 24, the net weight of the string of drill pipe P imposed on the drill bit, to force it against the bottom of the well bore can be regulated. This net weight is maintained constant provided the pressure of the liquid in the cylinder space 24 is maintained constant. In the use of the apparatus, the weight of the entire drill string P ordinarily will exceed the supporting weight of the liquid under pressure upon the upper cylinder head 11, the net weight imposed on the drill bit being the difference between the weight of the entire drill string and the unit pressure of the liquid in the cylinder space 24 acting over the area of the upper cylinder head 11. The pressure is maintained in the cylinder by the pump 20 and choke orifice 23, the cylinder it? still being capable of telescoping relative to the piston 14 and piston rod 15 without changing the lifting force on the string of drill pipe P. If, for example, the cylinder is ten feet in length, it may move a total of about ten feet with respect to the piston 14, and if the piston does not contact the cylinder head 11 and the pressure of the liquid in the cylinder space 24 is maintained constant, the imposition of a constant drilling weight on the drilling bit H will result.

The centrifugal pump Zti is operating constantly to force fluid into the cylinder Ill, the throttling action of the choke orifice 23 causing a back pressure of the desired value to be built up in the cylinder. The choke orifice 23, however, allows liquid pumped into the cylinder space 24 toreturn through the exhaust line 22 to the reservoir 19. By means of a suitable pressure gauge 25, the pressure in the cylinder 10 can be observed, and by varying the speed of the pump 26, this pressure can be changed by the operator, if desired.

Assuming the apparatus A to be installed on a floating drilling barge C, a constant drilling Weight is maintained on the drill bit H despite the undulating or vertical movement of the floating barge and of the derrick D mounted thereon. The apparatus permits lowering and elevating of the barge without correspondingly lowering and elevating the drill string P, in view of the ability of the piston 14 and cylinder 1%) to telescope with respect to one another, the pressure in the cylinder being maintained constant, inasmuch as the relative movement of the piston" 14 and the cylinder 10 either causes a discharge of liquid from the cylinder above the piston 14, or an increase in liquid supply in the cylinder, because of the action of the motor driven pump and the choke orifice 23.

As shown, the cylinder space 26 on the low pressure side of the piston 14 is open to atmosphere because of a drain hole 27 in the lower cylinder head 12. Thus, any liquid that might leak from the upper side of the piston 14- to its low pressure side is prevented from interfering with the telescopic movement of the cylinder with respect to the piston by being able to drop out through the drain hole 27.

The apparatus so far described is capable of maintaining a substantially constant drilling weight on the drill bit. However, in the event of a failure in the hydraulic system, as, for example, by a break occurring in the inlet line 21 or the outlet line 22, the hydraulic pressure would be lost and the cylinder 10 and the drill string P attached thereto would drop suddenly, an excess of drilling weight either being imposed on the drill bit H through the string of drill pipe P, or the upper cylinder head 11 being stopped suddenly by engaging the upper side of the piston 14, usually with an impact blow of substantial force. Damage to the equipment might result, which the present invention avoids. W i

As shown, the piston 14 and piston rod 15 are connected to a pair of retarding cylinders 30 of substantially the same length as the main compensating cylinder 19, as by means of a yoke 31 suitably secured to the upper ends of the retarding cylinders 3i and to the piston rod 15. The retarding or safety cylinders 34) each have a piston 32 disposed therein suitably secured to a piston rod 33 slidably through a lower safety cylinder head 34, the rods being appropriately connected to the compensating cylinder head 12, as by means of a yoke 35 secured to a rod or stem connection 13 extending from the lower compensating cylinder head 12, and also to the safety piston rods 33. The safety pistons 32 each have an orifice 37 extending longitudinally therethrough to permit a liquid in each safety cylinder 30 to pass from one side of the piston 32 to its opposite side as the piston 32 moves longitudinally in both directions in the cylinder. The entire cylinder 36, both above and below its piston 32, is completely filled with a suitable liquid, such as oil, the oil being prevented from leaking around the exterior of the piston by a suitable side seal or piston ring 38 on the latter slidably and sealingly engaging the wall of the cylinder 30.

Each orifice 37 has a sufficient area to permit ready transfer of liquid through the orifice from one side of the piston 32 to the other side of the piston as relatively slow movement between the pistons 32 and the cylinders 30 occurs. However, in the event that a rapid relative longitudinal movement of the pistons and the cylinders tends to occur, the necessity for the liquid on one side of each piston 32 to transfer through the orifice 37 to its other side prevents such rapid movement from occurring.

In the use of the apparatus illustrated in FIG. 2, and under normal conditions in drilling the well bore, the retarding or cushioning pistons 32 have no effect on the relative telescopic movement of the main compensating cylinder 10 with respect to its piston 14. The up and down movement of the drilling barge C occurs at a relatively slow rate, so that an upward movement of the compensating piston 14 and of the cushioning cylinders 30, for example, relative to the compensating cylinder 10 andthe cushioning pistons 32 can occur since the liquid below the cushioning pistons 32 have ample time to transfer through the orifices 37 into the cylinders on the upper side of the pistons 32. Similarly, relative lowering of the compensating piston 14 and of the cushioning cylinders 32 along the compensating cylinder 10 and cushioning pistons 32 can occur without restraint by the cushioning pistons 32, since the liquid in the upper part of the cylinders 30 have ample time to flow or transfer downwardly through the orifices 37 into the cylinder spaces below the pistons 32.

In the event of a break in the inlet line 21, for example, the pressure in the compensating cylinder 10 above its companion piston 14 would be lost and dissipated suddenly. As a result, the lifting force'on the upper cylinder head 11 would be lost, and the cylinder 10, together with the retarding pistons 32 connected thereto, would tend to drop suddenly under the weight of the string of drill pipe P hanging therefrom. Such sudden dropping cannot occur. In fact, downward movement of the cylinder 10 and the outer pistons 32 can only occur at a rate depending upon the time that it takes liquid in the outer cylinders Silbelow the pistons 32 to transfer through the orifices 37 to the cylinder spaces above the pistons 32. Instead of the dropping of the drill string P being able to occur at a rapid rate, it is lowered at a relatively slow rate, avoiding damage to the equipment. Moreover, such slow descent will eventually bring the upper cylinder head 11 into contact with the piston 14, which is supported by the traveling block T hanging from the crown block E, the contact between the upper cylinder head 11 and the piston 14 being brought about in a relatively slow manner and avoiding harmful impact blows therebetween, which might damage the equipment. Thus, the apparatus A is brought to a state of rest in a slow or retarded manner.

The form of invention illustrated in FIGS. 3 and 4 in many respects is essentially the same as the one shown in FIG. 2, and may be mounted in the rig in substantially the same location. However, sudden dropping of the drill string, P and compensating cylinder 10 is prevented in another manner, and without the provision of the orifices 37 through the shock-absorbing or retarding pistons. Instead, these pistons 32a are imperforate, their companion cylinders 3i however, being completely filled with a liquid, such as oil, both above and below the pistons. The upper end of each shock-absorbing cylinder 39 is connected to its lower end through a fluid transfer line 40 that contains a check valve 41, this check valve normally being biased to an open position and only shifting to a closed position when the rate of flow of fluid through it exceeds a predetermined value.

As shown in FIG. 4, the check valve 41 includes a valve body 42 suitably connected in the fluid transfer line 40 and having a central passage 43 surrounded by a valve seat 44. A companion check valve head 45 is movable upwardly into engagement with this seat 44 to prevent upward flow of fluid in the fluid transfer line 40, this head being guided in its movement to and from en agement wtih its seat by a suitable valve stem 46 slidable in the valve body 42. The valve head 45 is normally biased in a direction away from its seat, or held in an open position, by a suitable helical compression spring 47 encircling the stem, one end bearing against a spring seat 48 and its other end against the head 45 to maintain it oif its valve seat 44, the distance of the valve head from its seat being limited by a flange 49 on the stem engagin the valve body seat 48.

The spring 47 exerts a force suflicient to hold the valve head 45 from its seat 44 during normal operation of the apparatus. During such normal operation of the apparatus, the upward flow of fluid through the fluid transfer line 40 and around the valve head 45 tends to shift the valve head towards its seat, but the pressure differential of such fluid is insufficient to overcome the force of the spring 47. However, should there be a sudden increase in the velocity of the fluid flowing upwardly through a fluid transfer line 40, such fluid velocity, which is accompanied by an increased fluid pressure differential, will overcome the force of the spring 47 and shift the valve head 45 toward engagement with its seat 44, the pressure of the fluid in the fluid transfer line below the valve head 45 .then holding the valve head in engagement with its seat 44-to close and main tain closed the passage 43 through the Valve body 42.

In the event of an excessive drop in pressure in the compensating cylinder above its piston 14, the cylin der 1t) and the retarding or cushioning pistons 32a attached thereto would tend to drop suddenly, the retarding pistons tending to force the liquid in the cylinders 34 therebelow at a comparatively rapid rate upwardly through the fluid transfer lines 4% and around the valve heads 45. Such rapid flow of fluid would shift the valve heads upwardly against their seats 44 and prevent any further fluid from flowing out of the lower portions of the cushioning cylinders 30. Accordingly, the liquid in the cushioning cylinders below the pistons 32a would be trapped therein, preventing any further dropping of the pistons 32a, and of the cushioningcylinder 10 and drill pipe P connected thereto, relative to the traveling block T, which is supporting the shock-absorbing cylinders 30. As soon as one or both of the valves 41 closes, further downward movement of the running-in string P and of the cushioning cylinder 19 and retarding pistons 32a cannot occur, these parts being prevented, by the closing action of the valves, from moving any substanof fluid through the fluid transfer lines 40 between the upper and lower ends of the retarding cylinders 3t. Accordingly, there is no restriction to the telescopic movement of the cushioning cylinder 10 along the cushioning piston 14, which results from the rise and descent of the floating barge C. It is only when the velocity of fluid flowing through the valves 41 becomes excessive that such valves close and prevent any further descent of the cushioning cylinder 10 along its cushioning piston 14.

In the form of invention illustrated in FIGS. 5 to 8, inclusive, the same ultimate result is accomplished as with the apparatus illustrated in FIG. 3. As shown, the cushioning piston 14a is of annular shape, being slidable relatively in an annular cushioning cylinder 10a formed by an outer cylinder skirt 60 and an inner cylinder skirt or sleeve 61. The lower end of the outer skirt or sleeve 60 is threadedly attached to a lower cylinder head 12a, which is also true of the inner sleeve 61, the cylinder head having a suitable connection 13 tial distance, thereby preventing excess weight from being imposed on the drill pipe P to produce its kinking, and

the compensating cylinder head 11 from striking an im- 'pact blow against the compensating piston 14, or the retarding pistons 32a from striking an impact blow on their companion lower cylinder head.

With the apparatus illustrated in FIG. 3, the valves 41 are normally at a fully open position, providing a'large passage area for the flow of fluid through the valves, thereby avoiding any material restriction to the transfer for attachment to the rotary swivel S. The upper end of the annular cylinder 10a is closed by an annular cylinder head 11a, which may rest upon a split snap supporting ring 62 disposed in a groove 63 in the outer cylinder sleeve 60, the head being prevented from moving upwardly out of the cylinder by an upper snap retaining ring 64 disposed in a groove 65 in the outer sleeve. An external seal 66 sealingly engages the of the outer cylinder sleeve to prevent leakage between it and the cylinder head 11a, whereas, an inner seal ring 67 engages the periphery of the inner cylinder sleeve 61 to'prevent leakage between it and'the cylinder head 11a.

The annular piston 14a is supported from the hook I of the traveling block by a plurality of circumferentially spaced piston rods 15a which are threadedly or otherwise secured to the piston and which are slidable through the annular cylinder head 11a, the upper ends of these rods being attached to an appropriate upper connector 31:: which will be carried by the traveling hook I and block T. Leakage of fluid along the piston rods 15a is prevented by suitable rod packing or seal rings 69 carried by the annular cylinder head 11a and engaging the rods.

Fluid may be circulated through the annular cylinder 19a above the piston 14a in much the same manner as in the other forms of the invention. The fluid flows into the upper end of the annular cylinder ltla through the inlet .line 21 and flows out of the cylinder through the return line 22 connected to the reservoir 19, the fluid flowing through a choke orifice 23 in this return line in the same manner as illustrated in the other forms of the invention. A drain hole 27 is provided in the lower cylinder head 12a to prevent liquid accumulation in the low pressure side of the annular cylinder, which might interfere with appropriate ope-ration of the apparatus.

A retarding or cushioning piston 76 is reciprocabl in the inner central cylinder 61, this piston having a suitable seal ring 71 thereon sealingly engaging the wall of the inner cylinder member. A piston rod 72 is secured to this piston and extends upwardly through an upper cylinder head 73 closing the upper end of the inner cylinder member 61. As shown, the cylinder head 73 rests upon a split snap ring 74 mounted in the cylinder 61, being held thereagainst by an upper split snap ring 75 also secured within this cylinder. Leakage around the head '73 is prevented "by a seal ring 76 engaging the wall of the inner cylinder 61, whereas, leakage along the piston rod 72 is prevented by an inner seal ring 77 on the head sealingly engaging the periphery of the piston rod. This piston rod 72 is also connected to the upper connector 31a, which is supported from the hook I and the traveling block T.

The inner cylinder 61 is completely filled with a liquid both above and below the piston 76, the upper end of the inner cylinder being connected to its lower end by a fluid transfer line 40a that embodies a pressure volume check valve 41, which may be of the same type as used in the amazes form of invention shown in FIGS. 3 and 4. The check valve 41, however, will operate ina reverse direction, since its valve head 45 will move downwardlyinto engagement with its companion seat 44 when the velocity of fluid through the fluid transfer line 40a is capable oi: overcoming the valve opening force of the spring '47.

In the form of invention shown in FIGS. 5 to 8, inclusive, the drill pipe P is supported from the annular cylinder 19a, the load of the drill pipe being transferred from the upper annular cylinder head Ila through the liquid therebelow to the annular piston 14a, which is suppo-rted by the traveling block T and derrick equipment thereabove through the agency of the piston rods 15a slidable through the upper annular cylinder head 11a. The pressure of the fluid in the annular cylinder acting over the annular area of the cylinder head 11a determinestne lifting force of the apparatus A on the string of drill pipe P 'therebelow, and the drilling weight exerted by the drill pipe upon the drill bit H at the bottom of the hole B. As

the drilling barge C rises and falls, the annular cylinder 16a can telescope along the annular piston 14a, the pump 20 maintaining the annular cylinder above the piston 14a filled at all times with liquid at the appropriate constant pressure.

During the up and down movement of inder ltia along the annular piston 14a, the inner cylinder 61 is also moving upwardly and downwardly along the inner retarding or cushioning piston 7'8, causing liquid to transfer between the upper end of the central cylinder 61 and its lower end through the fluid transfer line 40a. Such transfer of liquid occurs in an unimpeded fashion during normal operation of the apparatus, since the spring 47 is maintaining the check valve 41 in its open condition. Accordingly, the comparatively large annular crosssectional area of the annular piston 14a and annular cylinder head 11a can readily efiect an appropriat supporting of the drill string P in tension without the liquid in the inner cylinder 61 assisting or opposing the support of the drill pipe by the annular portion of the apparatus. If, however, a break occurs in one of the hydraulic lines 21 or 22, to dissipate the pressure in the annular cylinder a, the cylinders Etta, 61 would tend to drop along the pistons 14a, 70, causing the liquid in the upper portion of the central cylinder 61 to flow out through th fluid transfer line 40a towards its lower portion. Such liquid will be flowing at a greatly increased velocity and will engage the valve head 45 and shift it downwardly against the force of the spring 47 into engagement with its seat 44, precluding any further transfer of liquid between the upper and lower portions of the central cylinder 61, trapping such liquid in the cylinder between the piston '70 and the upper central cylinder head 73. Such trapped liquid then prevents any further descent of the cylinders along the pistons, or with respect to the derrick D, in view of the support by the derrick of the piston devices through the crown block E, lines L and traveling block T. The weight of the drill pipe P is then being carried by the central piston '70, until appropriate manipulation of other equipment on the derrick occurs to relieve the load, as, for example, supporting the string of drill pipe through appropriate slips (not shown) in the rotary table R. After repair of the apparatus so that pressure can again be maintained within the annular cylinder 16a drilling can proceed with the apparatus A able to function as a telescopic joint, maintaining a constant support of a portion of the weight of the drilling string P, despite the up and down movement of the drilling barge C. Accordingly, the drilling weight imposed on the drill bit H at the bottom of the hol will remain constant.

The invention has been described particularly with respect to the drilling of a well bore. It can, however, be used in connection with drilling operations of various types in the well bore, and may be used to support any running-in string, such as a tubular string in tension, in the well bore regardless of the rise and fall of the drilling barge.

the annular cyl- I claim; V

1. In an apparatus for maintaining a predetermined stress in a running-in string disposed in a Well bore and which is supported by a rig: elongate cylinder means; piston means slidable longitudinally in said cylinder means; one of said means being adapted for operative connection to the running-in string; the other of said means beingadapted for operative connection to the rig; means for maintaining fluid under pressure in said cylinder means on one side of said piston means as said piston means and cylinder means move longitudinally relative to 'one another in both longitudinal directions, whereby the stress of said running-in string is transferred between said piston means and cylinder means to the rig; and means for restricting relative longitudinal movement between said cylinder means and piston means at an abnormal rate upon loss of pressure in said cylinder means and while said piston means is between the ends of its relative travel in said cylinder means. I 2. In an apparatus for maintaining a predetermined stress in a running-in string disposed in a well bore and which is supported by a rig: elongate cylinder means; piston means slidable longitudinally in said cylinder means; one of said means being adapted for operative connection to the running-in string; the other of said means being adapted for operative connection to the rig; means for maintaining fluid under pressure in said cylinder means on one side of said piston means as said piston means and cylinder means move longitudinally relative to one another in both longitudinal directions, whereby the stress of said running-in string is transferred between said piston means and cylinder means to the rig;

'and hydraulically operable means responsive to relative longitudinal movement between said cylinder means and piston means at an abnormal rate for restricting such relative longitudinal movement upon loss of pressure in said cylinder means.

3. In an apparatus for maintaining a predetermined stress in a running-in string disposed in a well bore and :which is supported by a rig: elongate compensating cylinder means; compensating piston means slidable longitudidaily in said cylinder means; one of said means being adapted for operative connection to the running-in string; the other of said means being adapted for operative connection to the rig; means for maintaining fluid under pressure in said cylinder means on one side of said piston means as said piston means and cylinder means move longitudinally relative to one another in both longitudinal directions, whereby the stress of said running-in string is transferred between said piston means and cylinder means to the rig; elongate retarding cylinder means connected to one of said compensating means; retarding piston means slidable longitudinally in said retarding cylinder means and connected to the other of said compensating means; a liquid in said retarding cylinder means on opposite sides of said retarding piston means; and means for controllably conducting said liquid between regions of said retarding cylinder means on opposite sides of said retarding piston means, whereby said retarding piston means and retarding cylinder means restrict relative longitudinal movement between said compensating cylinder means and compensating piston means at an abnormal rate.

4. In an apparatus for maintaining a predetermined stress in a running-in string disposed in a well bore and which is supported by a rig: elongate compensating cylinder means; compensating piston means slidable longitudinally in said cylinder means; one of said means being adapted for operative connection to the running-in string; the other of said means being adapted for operative connection to the rig; means for maintaining fluid under pressure insaid cylinder means on one side of said piston ineans as said piston means and cylinder means move longitudinally relative to one another in both longitudinal directions, whereby the stress of said running-in string is transferred between said piston means and cylinder means to the rig; elongate retarding cylinder means connected to one of said compensating means; retarding piston means slidable longitudinally in said retarding cylindermeans and connected to the other of said compensating means; a liquid in said retarding cylinder means on opposite sides of said retarding piston means; and a flow restricting orifice through said retarding piston means through which said liquid is conducted between regions of said retarding cylinder means on opposite sides of said retarding piston means, whereby said retarding piston means and retarding cylinder means restrict relative longitudinal movement between said compensating cylinder means and compensating piston means at an abnormal rate.

5. In an apparatus for maintaining a predetermined stress in a running-in string disposed in a well bore and which is supported by a rig: elongate compensating cylinder means; compensating piston means slidable longitudinally in said cylinder means; one of said means being adapted for operative connection to the running-in string; the other of said means being adapted for operative connection to the rig; means for maintaining fluid under pressure in said cylinder means on one side of said piston means as said piston means and cylinder means move longitudinally relative to one another in both longitudinal directions, whereby the stress of said running-in string is transferred between said piston means and cylinder means to the rig; elongate retarding cylinder means connected to one of said compensating means; retarding piston means slidable longitudinally in said retarding cylinder means and connected to the other of said compensating means; a liquid in said retarding cylinder means on opposite sides of said retarding piston means; and means comprising flow restricting means through which said liquid is conducted between the regions of said retarding cylinder means on opposite sides of said retarding piston means, whereby said retarding piston means and retarding cylinder means restrict relative longitudinal movement between said compensating cylinder means and compensating piston means at an abnormal rate.

6. In an apparatus for maintaining a predetermined stress in a running-in string disposed in a well bore and which is supported by a rig: elongate compensating cylinder means; compensating piston means slidable longitudinally in said cylinder means; one of said means being adapted for operative connection to the running-in string; the other of said means being adapted for operative connection to the rig; means for maintaining fluid under pressure in said cylinder means on one side of said piston means as said piston means and cylinder means move longitudinally relative to one another in both longitudinal directions, whereby the stress of said running-in string is transferred between said piston means and cylinder means to the rig; elongate retarding cylinder means connected to one of said compensating means; retarding piston means slidable longitudinally in said retarding cylinder means and connected to the other of said compensating means; a liquid in said retarding cylinder means on opposite sides of said retarding piston means; means for conducting said liquid between regions of said retarding cylinder means on opposite sides of said retarding piston means, said conducting means including a check valve adapted to remain open during flow of said liquid through the conducting means in one direction at rates below a predetermined value but which is adapted to be closed by flow of said liquid through the conducting means in said one direction at a rate exceeding said predetermined value, whereby said retarding piston means and retarding cylinder means restrict relative longitudinal movement between said compensating cylinder means and compensating piston means at an abnormal rate.

7. In apparatus for maintaining a predetermined stress in a running-in string disposed in a Well bore and which is supported by a rig: elongate annular cylinder means; annular piston means slidable longitudinally in said cylinder means; one of said means being adapted for operative connection to the'running-in string; the other of said means being adapted for operative connection to the rig; means for maintaining fluid under pressure in said cylinder means on one side of said piston means as said piston means and cylinder means move longitudinally relative to one another in both longitudinal directions, whereby the stress of said running-in string is transferred between said piston means andcylinder means-to the rig; elongate retarding cylinder means within said annular cylinder means and connected to one of said annular means; retarding piston means slidable longitudinally in said retarding cylinder means and connected to the other of said annular means; a liquid in said retarding cylinder means; and means for controllably conducting said liquid between regions of said retarding cylinder means on 0pposite sides of said retarding piston means, whereby said retarding piston means and retarding cylinder means restrict relative longitudinal movement between said annular cylinder means and annular piston means at an abnormal rate.

8. In apparatus for maintaining a predetermnied stress in a running-in string disposed in a well bore and which is supported by a rig: elongate annular cylinder means; annular piston means slidable longitudinally in said cylinder means; one of said means being adapted for operative connection to the running-in string; the other of said means being adapted for operative connection to the rig; means for maintaining fluid under pressure in said cylinder means on one side of said piston means assaid piston means and cylinder means move longitudinallyrela-tive to one another in both longitudinal directions, whereby the stress of said running-in string is transferred between said piston means and cylinder means to the rig; elongate retarding cylinder means Within said annular cylinder means and connected to one of said annular means; retarding piston means slidable longitudinally in said retarding cylinder means and connected to the other of said annular means; a liquid in said retarding cylinder means; means for conducting said liquid between regions of said retarding cylinder means on opposite sides of said retarding piston means, said conducting means including a check valve adapted to remain open during flow of said liquid through the conducting means in one direction at rates below a predetermined value but which is adapted to be closed by flow of said liquid through the conducting means in said one direction at a rate exceeding said predetermined value, whereby said retarding piston means and retarding cylinder means restrict relative longitudinal movement between said annular cylinder means and annular piston means at an abnormal rate.

9. In apparatus for maintaining a predetermined stress in a running-in string disposed in a well bore and which is supported by a rig: elongate annular cylinder means; annular piston means slidable longitudinally in said cylinder means; one of said means being adapted for operative connection to the running-in string; the other of said means being adapted for operative connection to the rig; means for maintaining fluid under pressure in said cylinder means on one side of said piston means as said piston means and cylinder means move longitudinally relative to one another in both longitudinal directions, whereby the stress of said running-in string is transferred between said piston means and cylinder means to the rig; elongate retarding cylinder means within and connected to said annular cylinder means; retarding piston means slidable longitudinally in said retarding cylinder means and connected to said annular piston means; a liquid in said retarding cylinder means; and means for controllably conducting said liquid between regions of said retarding cylinder means on opposite sides of said retarding piston means, whereby said retarding piston means and retarding cylinder means restrict relative longitudinal movement between said annular cylinder means and annular piston means at an abnormal rate.

'10. In apparatusfor maintaining apredetermined stress in a running-in-string'disposed in a-well bore and which is supportedby a-rig: aelongate annular cylinder means; annular piston meansslidable longitudinally in saidcylinder means; one of saidrneans being adapted for operative connection to the running-in string; the other of said means being adapted for operative connectionto the-rig; means for maintaining fluid under pressure, in said cylinder means on one side of said ;piston means as said piston means andcylinder means move longitudinallyrelative to one another in both longitudinal directions, whereby the stress of said running-in-string is transferred between said piston means and cylinder means to theriggelongate retarding cylinder means'within and connected tosaid annular cylinder means; retarding piston means slidable longitudinally in saidretardingcylinder means and connected to said annular piston means; a liquid in said retarding cylinder means; means'for conducting said liquid between regions of said retarding cylinder means on opposite sides of said retarding piston means, said conducting means including a check valve adapted to remain open during flow 12 of said liquidthrough the conducting means in one direction at rates below a predetermined value but which is adapted to :be closed by flow of said liquid through the conducting means in said one direction at a rate exceeding said predetermined value, whereby said retarding piston means and retarding cylinder means restrict relative longitudinal movement between said annular cylindermeans and annular piston means at an abnormal rate.

:References ,Cited in the file of this patent UNITED STATES PATENTS 512,313 McDonald Jan. 9, 1894 1,998,873 Kingsbury Apr. 23, 1935 2,605,751 Perry et al Aug. 5, 1952 2,775,015 Erb Dec. 25,1956 2,838,140 Ramusson et al. June 10, 1958 2,857,138 'Svendsen ,et al Oct. 21, 1958 2,945,677 Kammerer July 19, 1960 3,081,743 Bishopet al. Mar. 19, 1963 

1. IN AN APPARATUS FOR MAINTAINING A PREDETERMINED STRESS IN A RUNNING-IN STRING DISPOSED IN A WELL BORE AND WHICH IS SUPPORTED BY A RIG: ELONGATE CYLINDER MEANS; PISTON MEANS SLIDABLE LONGITUDINALLY IN SAID CYLINDER MEANS; ONE OF SAID MEANS BEING ADAPTED FOR OPERATIVE CONNECTION TO THE RUNNING-IN STRING; THE OTHER OF SAID MEANS BEING ADAPTED FOR OPERATIVE CONNECTION TO THE RIG; MEANS FOR MAINTAINING FLUID UNDER PRESSURE IN SAID CYLINDER MEANS ON ONE SIDE OF SAID PISTON MEANS AS SAID PISTON MEANS AND CYLINDER MEANS MOVE LONGITUDINALLY RELATIVE TO ONE ANOTHER IN BOTH LONGITUDINAL DIRECTIONS, WHEREBY THE STRESS OF SAID RUNNING-IN STRING IS TRANSFERRED BETWEEN SAID PISTON MEANS AND CYLINDER MEANS TO THE RIG; AND MEANS FOR RESTRICTING RELATIVE LONGITUDINAL MOVEMENT BETWEEN SAID CYLINDER MEANS AND PISTON MEANS AT AN ABNORMAL RATE UPON LOSS OF PRESSURE IN SAID CYLINDER MEANS AND WHILE SAID PISTON MEANS IS BETWEEN THE ENDS OF ITS RELATIVE TRAVEL IN SAID CYLINDER MEANS. 